1. Field of the Invention
The present invention relates to an information recording medium in which information is recorded as recording marks such as pits.
2. Description of the Related Art
Currently, an optical disk typified by a CD and a DVD has been put into practice. In the optical disk, information is recorded as the length of pits. However, there is the desire to reserve different recording space without reducing recording space for pits, for example, in order to record information for copy control for the sake of inhibiting illegal copy, etc.
A proposal to vary positions of pits in the radius direction of the optical disk is presented as a method of increasing recording space by a means except the one of using the length of pits. In this technique, the positions of pits is wobbled in the radius direction of the optical disk, and then in formation is recorded by means of FM modulating the wobble.
However, when reproducing a wobble signal recorded by means of varying the positions of pits, crosstalk and so on enters the wobble signal. The crosstalk is caused by wobble from an adjacent track or an RF signal recorded by means of the length of pits. Hence, the wobble signal has a degraded CN (Carrier to Noise ratio), a problem occurs on reading of address information recorded by FM modulation and so on, and the reference signal extracted from the wobble signal becomes inaccurate. Further, in the case of a multilayer disk as well, the same problem results from crosstalk of a wobble signal between layers. Hence, it is difficult to accurately perform writing in the multilayer disk.
As described above, in the conventional method, since a frequency for recording leans to a specific one (wobbling frequency), when the track is affected by noise and crosstalk, it is difficult to detect a signal with accuracy.